The present invention relates to apparatus for recording and/or reading information on an optically readable disc which apparatus comprises: a frame; a carrier which is movable relative to the frame along a first axis; first electrodynamic drive means for driving the carrier along the first axis; a lens system which is arranged on the carrier and which is movable relative thereto along a second axis perpendicular to the first axis; second electrodynamic drive means for driving the lens system along the second axis; and a lens system-supporting arrangement comprising supporting means arranged between the carrier and the lens system. Herein "frame" is to be understood to mean that part of the apparatus with which the carrier co-operates directly via the first electrodynamic drive means. The frame itself may also be movable relative to another part of the apparatus. The term "lens system" is to be understood to mean a system comprising at least one lens. The lens system may comprise, for example, a bodily movable objective but it may alternatively form a part of an objective whose other part may be rigidly connected to the carrier.
Apparatus as described above is known in various versions, for example, in optical video-disc players, optical audio-disc players or peripheral computer equipment for the storage and reproduction of information an optical storage discs. In all these devices, the lens system is movable along the focusing axis in order to enable movements of the information surface, which inevitably occur during rotation of the disc, to be followed accurately with the laser beam which is formed to a read spot. This is necessary because the depth of focus of the lens systems used is of the order of magnitude of a few microns only. Therefore, there must be provided one or more supporting arrangements which permit the focusing movements of the lens system and, depending on the construction of the apparatus, permit radial movements for following the track and tangential movement for correcting time errors. The supporting arrangements inhibit undesired movements of the lens system. The radial travel of the carrier on which the lens system is arranged is such that the read spot can reach every track on the optically readable disc. For the rapid location of a track, or for rapidly finding a blank part of the optically readable disc in order to record information in this part, it is important that the slide can be moved rapidly along the radial path. Since the lens system has a certain mass, radial forces are exerted on the lens system during the fast radial movements of the carrier, which forces may be of an amplitude such that problems may arise when the lens system is simultaneously moved along the focusing axis, perpendicularly to said path. Depending on the type of lens system supporting arrangement used, these problems may be friction problems and bandwidth problems. This will be explained in more detail with reference to some known devices of the afore-mentioned type.
Applicant's U.S. patent application Ser. No. 471,972, filed Mar. 4, 1983, now U.S. Pat. No. 4,443,721 (herewith incorporated by reference), describes a device in which the lens system comprises an objective which is movably supported on the carrier by means of a plurality of blade springs which extend in the same direction as the first axis. The carrier comprises a translating slide. The bandwidth for the slide drive is limited because at high frequencies the blade springs are no longer sufficiently rigid in the direction of translation. The deformation of the blade springs then gives rise to movements of the objective relative to the slide in the direction of translation.
It is also known, for example from U.S. Pat. No. 4,021,101, herewith incorporated by reference, to use a sleeve supporting arrangement for the lens system. The lens system is an objective which is movable in a supporting sleeve, which inevitably gives rise to some friction. The objective is movable relative to a translating slide. In the case of slow or uniform translational movements of the slide this friction is very low because no forces act on the objective in the direction of translation and, consequently, in a direction normal to the friction surfaces of the lens-system supporting arrangement. This is different if the slide must be moved with high accelerations and decelerations. The frictional forces then occurring depend directly on the accelerations and decelerations of the slide movement. Both the movements of the objective along the focusing axis and the movements of the slide are controlled by electronic servo-circuits. The variable friction in a focusing supporting arrangement gives rise to cross-talk between the two servo-circuits. Another problem is caused by the radial clearance between the objective and the sleeve. Tracking becomes more difficult when radial forces are exerted on the objective because then the objective does not occupy a well-defined position in the sleeve but is urged either against one wall or against the other wall, depending on the direction of movement of the slide. This may be precluded by providing in a prestress in the lens-system supporting arrangement. However, this leads to an increase of the friction in the supporting arrangement, which is undesirable for several reasons, whilst the modulation of the frictional force as a result of the accelerations and decelerations of the slide persists.